The US Army has apologised for any distress caused after new images of US troops posing with the bodies of Afghan civilians were published in a magazine.
In a statement, the US Army said the photos in Rolling Stone magazine were disturbing and contrary to its values.
Similar photos appeared in German paper Der Spiegel last week. The killings apparently took place early last year.
The US Army is in the midst of courts martial of those allegedly involved, one of whom was jailed last week.
According to executive editor Eric Bates, Rolling Stone magazine obtained about 150 photos in all, and posted 17 of them on its website.
Also posted are two videos allegedly showing US attacks on Afghans.
Bates would not say how the magazine obtained the photographs.
Responding to their publication, the US Army said it would "relentlessly" pursue the truth, no matter how difficult or lengthy the investigation.
"The photos published by Rolling Stone are disturbing and in striking contrast to the standards and values of the US Army," it said in a statement.
"Like those published by Der Spiegel, the Army apologises for the distress these latest photos cause.
"Accountability remains the Army's paramount concern in these alleged crimes, and we continue to investigate leads."
'Rogue army unit'
The photographs are alleged to have been taken by a "rogue" US Army unit in Afghanistan in 2010.
They feature US soldiers grinning over the corpses of Afghan civilians they had allegedly killed.
Specialist Jeremy Morlock was sentenced last week to 24 years in prison for his part in the killing of unarmed Afghan men.
Under a plea deal he is expected to testify against four comrades also to be tried over the killings last year in Kandahar province.
"The plan was to kill people," Morlock told a military judge during his trial.